This application claims priority under 35 U.S.C. § 119(a) to Patent Application No. 2004-049802 filed in Japan on 25 Feb. 2004, the content of which is hereby incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to a circuit device comprising LC resonant circuit(s) that increase circuit impedance(s).
2. Description of the Related Art
Such circuit devices employ LC resonant circuit(s) so as to increase circuit impedance(s) as seen from the input side and/or the output side of the circuit.
For example, as shown in FIG. 6, LC resonant circuit 103, in which coil 101 and capacitor 102 are connected in parallel, might be inserted between input terminal 104 and low-impedance circuit 105, and the resonant frequency of LC resonant circuit 103 might be made to agree with the frequency of a pulsed signal which is input thereto from input terminal 104. Upon input of a pulsed signal from input terminal 104, LC resonant circuit 103 resonates, displaying high impedance and increasing impedance as seen from input terminal 104. This makes it possible to treat input terminal 104 as if it was separated from the circuit impedance of low-impedance circuit 105 and connected only to high-impedance circuit 106 (see Japanese Patent Application Publication Kokai No. 2003-46357).
However, while it may be sufficient to simply insert a single LC resonant circuit in front of or behind the circuit impedance when there is only a single circuit impedance, there will as shown in FIG. 7 be a plurality of LC resonant circuit coils 111, 112 mounted on printed wiring board 113 where it is necessary to increase multiple circuit impedances through employment of respective LC resonant circuits. And what is more, due to constraints on the size of printed wiring board 113 it may be necessary to arrange respective coils 111, 112 in close proximity. Where this is the case, lines of magnetic force S1, S2 from respective coils 111, 112 will mutually overlap, and respective coils 111, 112 will be mutually electromagnetically coupled. This being the case, the inductances of these coils 111, 112 will change, and the impedances of respective LC resonant circuits will change. This has led to lowering of impedance as seen from input terminal 104.
Furthermore, even where there is only a single LC resonant circuit, lines of magnetic force from the coil of the LC resonant circuit can be disturbed due to the influence of peripheral components; and where this is the case, the inductance of the coil will change, and the impedance of the LC resonant circuit will change.
Moreover, where the current drawn by the circuit device(s) is large (500 mA or greater), the current which flows through the LC resonant circuit(s) will also be large. Under such circumstances, it will be necessary to increase the size of the coil core(s) and/or to increase the diameter of the wire used in the coil(s), increasing the size and weight of the coil(s) itself or themselves. Such a coil of large size and weight has the disadvantage of being easily damaged, as it will be susceptible to damage upon impact when dropped or the like.